1. Field of the Invention
The present invention relates to an optical mouse having a dynamic range, and more particularly to an optical mouse having a dynamic range, which is capable of adjusting an input range of an analog/digital (A/D) converter on the basis of a magnitude variation of an output signal from the A/D converter to increase a resolution of the A/D converter relative to a low illumination range or fine illumination range, thereby improving the ability of the converter to sense a fine signal variation.
2. Description of the Related Art
An optical mouse generally comprises an image sensor for sensing an image of a motion and outputting the resulting image signal, an A/D converter for converting the image signal from the image sensor into digital data, an image processor for performing a signal processing operation for the digital data from the A/D converter to detect the motion therefrom, and a controller for providing data corresponding to the detected motion to a computer.
Note that the A/D converter in the optical mouse has a fixed input range. With the A/D converter having the fixed input range, the optical mouse can desirably obtain a relatively accurate image in the case of inputting a signal of an amount of light within a certain range, but has the disadvantage of being incapable of obtaining an accurate image in the case of inputting a signal of an amount of light beyond the certain range. In order to make up for this problem, automatic gain control means is generally used to limit a signal magnitude of input light to the optical mouse.
FIG. 1 is a block diagram showing a circuit construction of a conventional optical mouse. As shown in this drawing, the conventional optical mouse comprises a light source 11 for emitting light to an object 1 such as a mouse pad, an image sensor 12 for sensing an image of the object 1, a shutter/controller unit 13 for limiting the magnitude of the image signal from the image sensor 12, an A/D converter 14 for converting an analog image signal from the shutter/controller unit 13 into digital image data, an image data processor 15 for processing the image data from the A/D converter 14 to detect motion data therefrom, and a system controller 16 for sending the motion data from the image data processor 15 to a computer.
In the above-mentioned conventional optical mouse, an input signal under the condition of an appropriate illumination or of incident light of high intensity has such a sufficient variation as to be converted according to a predetermined resolution of the A/D converter. Alternatively, where the incident light is small in amount, the shutter is opened for a period of time long enough to adjust a dark object to a proper brightness, but the input signal becomes that much smaller in variation. In other words, the dark object is extremely small in reflected light amount, resulting in there being a very small difference between a noise level and a signal level. As a result, provided that a signal incoming from the object is amplified, it will become a signal as shown in FIG. 2a because a noise level is also amplified, although the figure of the object is well visible. If the object is accurately centered on the image sensor, this sensor will provide a signal distribution as shown in FIG. 2b. For the effective detection of a motion by the optical mouse, it is preferable that a detected signal has a magnitude distributed uniformly over the entire input range of the A/D converter. However, in the case where the detected signal is under the condition of a low illumination, the magnitude thereof leans to a certain level of the entire input range of the A/D converter, or a low level.
By opening the shutter for a lengthy period of time under the above condition, the signal magnitude can be increased from a signal distribution SD1 to SD2 as shown in FIG. 2c. It is preferable that the detected signal varies over the entire input range of the A/D converter, but it varies over a small range under the condition of a low illumination. This signifies that an 8-bit A/D converter provides its output signal having a variation of, for example, 4 bits.
In other words, the magnitude of the detected signal input to the A/D converter 14 varies with an image, or light and dark regions on the pad for the optical mouse. Where the light and dark regions of the pad have a low contrast, the magnitude of the detected signal is distributed concentratedly (referred to hereinafter as xe2x80x98data concentrated distributionxe2x80x99) at a certain level of the entire input range of the A/D converter 14. For example, the data concentrated distribution may be present at any one of a high level, middle level and low level of the entire input range of the A/D converter 14.
Provided that the data concentrated distribution occurs as described above, the data magnitude will have a fine variation, thereby making it difficult for the optical mouse to detect a motion. In this case, there is a need for a technique to adjust the input range of the A/D converter about the level at which the data concentrated distribution occurs, thereby enabling the optical mouse to detect a fine motion.
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide an optical mouse having a dynamic range, which is capable of adjusting an input range of an analog/digital converter on the basis of a magnitude variation of an output signal from the analog/digital converter to increase a resolution of the analog/digital converter relative to a low illumination range or fine illumination range, thereby improving the ability of the converter to sense a fine signal variation.
In accordance with the present invention, the above and other objects can be accomplished by the provision of an optical mouse having a dynamic range, comprising analog/digital (A/D) conversion means having an input range adjusted based on an input range control signal, the A/D conversion means receiving an input signal over the adjusted input range and converting the received signal into digital data; and image data processing means for determining on the basis of image data from the A/D conversion means whether a data concentrated distribution has occurred, detecting a level of the input range with the data concentrated distribution upon determining that the data concentrated distribution has occurred, outputting the input range control signal to the A/D conversion means according to the detected level and processing the image data from the A/D conversion means to detect motion data therefrom.
Preferably, the image data processing means may subdivide a data concentrated distribution degree (data concentration degree) related to a magnitude variation of a detected signal and determine the input range of the A/D conversion means on the basis of the data concentration degree. In this case, the input range of the A/D conversion means can be adjusted more precisely centering around a data concentrated distribution area. Further, the resolution of the A/D conversion means is applied to a small, adjusted input range relative to the entire input range of the A/D conversion means, so that it can be increased relatively. Therefore, the A/D conversion means can detect a fine magnitude variation of the detected signal.